Medical screw and method of installation

ABSTRACT

A medical screw includes a shaft having a threaded portion and a distal guiding tip for introducing the screw into a pre-drilled implantation site. The threaded portion of the medical screw has a first series of helical threads having a first diameter and a second series of helical threads interleaved with the first series of helical thread and having a second diameter, where the first diameter is different than the second diameter. In addition, the medical screw may have a counter-rotation channel configured to receive bone growth.

TECHNICAL FIELD

[0001] This invention generally relates to methods and apparatus forfastening fractured bones and for attaching soft tissue to bone tissue.More particularly, this invention relates to a surgical medical screwhaving a “Hi-Lo” thread configuration for increasing the pulloutstrength of the screw, a distal guiding tip for guiding the screw into apre-drilled implantation site, and a counter-rotation device forresisting loosening of the screw from the implantation site.

BACKGROUND OF THE INVENTION

[0002] Medical screws are commonly used for a variety of surgicalprocedures. Medical screws may be used as suture anchors to attach asuture to a bone so that the suture may be used to hold soft tissue,such as torn tendons or ligaments, adjacent to the bone. Medical screwsmay also be used as fastening devices to attach prosthetics such asfixation plates to bone or to join portions of a fractured bone to aidthe healing process. The multiple threads of such medical screws improvesurgical repair by increasing the “pullout strength” of the screw, thatis, the screw's ability to resist being pulled out from the bone. Thethreads also reduce the time and force required to implant the screwinto the bone.

[0003] Various medical screws have been used for attaching objects, suchas sutures, plates, or other bone fragments, to bone. U.S. Pat. No.5,743,914 (Skiba) teaches a bone screw having a head for receiving ascrew driving device, a shaft having a first series of helical threadshaving a first diameter and a first pitch, and second series of helicalthreads interleaved with said first series of helical threads and havinga second diameter and a second pitch, wherein the second diameter issubstantially different than the first diameter and at least one of saidfirst and second pitches changes along the length of the shaft. Thisbone screw exhibits increased pullout strength and is particularlyuseful for joining bone fragments or for anchoring prosthetics to bone.

[0004] U.S. Pat. No. 5,087,201 (Mondani et al.) discloses aself-threading pin which is screw-threaded into the maxilla bone forimplantation of a dental prosthetic. The pin has a screw-threaded shankportion, a driving head at one end of the shank portion and a drill bitat the other end of the shank portion. The screw-threaded shank portionof the pin has two intercalated screw threads of different heights.

[0005] All of the bone screws disclosed in the prior art generallyutilize standard helical thread configurations. The above-describedprior art further discloses thread configurations having two differenthelical threads of different heights interleaved with each other.However, often times these screws are difficult to insert in apre-tapped/pre-drilled implantation site because there is no guidingmechanism which aids in aligning the screw with the implantation site.Further, the screws of the prior art are apt to counter-rotate, therebybecoming loose from the implantation site.

[0006] A medical screw is thus needed which overcomes the shortcomingsof the prior art.

SUMMARY OF INVENTION

[0007] A medical screw device according to the present inventionaddresses many of the shortcomings of the prior art.

[0008] In accordance with one aspect of the present invention, a medicalscrew comprises a head for receiving a screw driving device and a shaftextending from the head. The shaft generally includes respectivealternating first and second helical threads running substantiallyparallel with each other along the shaft (i.e., not intersecting).Additionally, in accordance with the present invention, the secondseries of helical threads advantageously exhibits a diameter differentthan the diameter of the first series of helical threads.

[0009] In accordance with an alternative embodiment of the presentinvention, the medical screw may comprise a plurality of series ofhelical threads, each exhibiting different diameters from the others. Inaccordance with this embodiment, the plurality of series of threadsalternate and run substantially parallel with each other along the screwshaft.

[0010] In accordance with another aspect of the present invention, themedical screw may be configured with a variety of different head typesand shapes.

[0011] In accordance with yet another aspect of the present invention,the medical screw may be manufactured from any type of bio-compatiblematerial, for example, titanium alloy, stainless steel, class siximplant grade plastic or a material made from bioabsobables such aspolyglycolic acid and the like.

[0012] In accordance with yet another aspect of the present invention,the medical screw can exhibit any length, and the diameters of theshaft, the first series of threads and the second series of threads maydiffer for different types and sizes of the bone in which the screw isto be used.

[0013] In accordance with yet another aspect of the present invention,the medical screw comprises a distal guiding tip that aids in theinsertion of the screw into a pre-tapped/pre-drilled implantation sitein bone tissue.

[0014] In accordance with still another aspect of the present invention,the thickness of the first and/or second series of threads decreasesalong the shaft of the screw.

[0015] In accordance with yet another aspect of the present invention,the head of the medical screw comprises at least one eyelet forreceiving a suture or multiple sutures.

[0016] In accordance with yet another aspect of the present invention,the medical screw comprises counter-rotation mechanisms for resistingloosening of the screw from the implantation site.

[0017] In accordance with still another aspect of the present invention,the Hi-Lo thread configuration may comprise a single, contiguous threadchanging in height along the shaft of the screw.

[0018] These and other aspects of the present invention will become moreapparent to those skilled in the art from the following non-limitingdetailed description of preferred embodiments of the invention takenwith reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0019] Exemplary embodiments of the present invention will hereafter bedescribed in conjunction with the appended drawing figures, wherein likedesignations denote like elements, and:

[0020]FIG. 1 is a side view of an exemplary embodiment of the medicalscrew of the present invention;

[0021]FIG. 2a is a schematic view of an exemplary embodiment of themedical screw of the present invention connected to a driver andinserted into tissue;

[0022]FIG. 2b is a schematic view of an exemplary embodiment of themedical screw of the present invention connected to a driver and alignedwith a pre-drilled implantation site;

[0023]FIG. 3 is a schematic view of an exemplary embodiment of themedical screw of the present invention showing the distal guiding tipinserted into a pre-drilled implantation site;

[0024]FIG. 4a is a side view of another exemplary embodiment of themedical screw of the present invention having a counter-rotationchannel;

[0025]FIG. 4b is a top view of the exemplary embodiment of the medicalscrew of the present invention as shown in FIG. 4a;

[0026]FIGS. 5a-5 e are side and top views of alternative embodiments ofthe medical screw of the present invention having counter-rotationchannels;

[0027]FIGS. 6a-6 c are side views of counter-rotation teeth of thepresent invention;

[0028]FIG. 7 is a side view of another exemplary embodiment of themedical screw of the present invention;

[0029]FIG. 8 is a side view of yet another exemplary embodiment of themedical screw of the present invention;

[0030]FIG. 9 is a side view of still yet another exemplary embodiment ofthe medical screw of the present invention; and

[0031]FIG. 10 is a side view of another exemplary embodiment of themedical screw of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The following description is of exemplary embodiments only and isnot intended to limit the scope, applicability or configuration of theinvention in any way. Rather, the following description provides aconvenient illustration for implementing exemplary embodiments of theinvention. Various changes to the described embodiments may be made inthe function and arrangement of the elements described without departingfrom the scope of the invention as set forth in the appended claims.

[0033] Referring now to FIG. 1, an exemplary embodiment of a medicalscrew 100 suitably comprises a shaft 102 and a head 104. Shaft 102 issuitably integral with head 104 and, in an exemplary embodiment, issubstantially cylindrical in shape. However, in accordance with afurther embodiment of the invention, shaft 102 may exhibit any suitableconfiguration. For example, referring momentarily to FIG. 7, shaft 102may be tapered. That is, the diameter of the shaft may get larger towardthe head of the screw. Shaft 102 may be configured to exhibit any lengthdepending on the nature and type of bone it is intended to be used withor the purpose for which it is being used.

[0034] Referring again to FIG. 1, shaft 102 further comprises a threadportion 106 proximate to head 104 and a distal guiding tip 108. Threadportion 106 and distal guiding tip 108 are separated by an imaginaryplane 110 perpendicular to a longitudinal axis 112 of shaft 102. Inaccordance with an exemplary embodiment of the present invention, threadportion 106 of shaft 102 may comprise two threads, major threads 114 andminor threads 116. In the illustrated embodiment, threads 114 and 116are each suitably arranged in a helical pattern and run substantiallyparallel to one another, alternating along shaft 102 of screw 100.However in accordance with a further embodiment of the invention, threadportion 106 may comprise one, two, three or more threads, also of ahelical pattern and interleaved in a suitable manner.

[0035] Distal guiding tip 108 of shaft 102 may be tapered to a point or,as in the illustrated embodiment, may terminate in a beveled tip 118 forpre-tapped applications that employ conventional pre-tappingmethodologies (e.g. pre-drilling and the like). It should beappreciated, however, that self-tapping or self-drilling endconfigurations may be used; for example, tapping flutes or the like. Asdiscussed more fully below, distal guiding tip 108 serves as a guidingor alignment device, aiding the surgeon in guiding and aligning screw100 to a pre-tapped/pre-drilled implantation site.

[0036] Threads 114 and 116 are oriented in an alternating or interleavedthread pattern with different diameters in a so-called “Hi-Loconfiguration.” As will be appreciated, such a configuration includesminor threads having a height H measured from the surface of shaft 102of between about 5% to about 99% and more preferably between about 25%to about 75%, and most preferably about 50% of the height of the majorthreads. Such a configuration with bone screws is believed to offeradvantages over other bone screw configurations because it allows forgreater recruitment of bone material, and particularly of the softcancellous bone matter which is typically the part of the bony anatomyto which many screws fasten. Also, the Hi-Lo thread configuration of thepreferred embodiment increases the shear strength near the outer edgesof the major threads, thus further increasing the pullout strength ofthe screw. Finally, because only half of the threads have a largeheight, the amount of torque required to drive/set the screw tends to bereduced. While FIG. 1 shows two thread series 114, 116, it mayappreciated that screw 100 may have one contiguous thread that changesin height along shaft 102.

[0037] With continuing reference to FIG. 1, threads 114 and 116 haveequal and constant pitch along thread portion 106. As used herein,“pitch” is defined as the distance from the center of one thread to thecenter of the next thread. This applies no matter whether the screw hasone, two, three or more series of threads. As may be appreciated, thepitch of at least one of the series of threads may vary along shaft 102.Because the pitches of the threads on multi-thread screws is less than asingle thread screw, fewer revolutions are necessary to implant thescrew. Consequently, the surgeon can insert the screw into bone faster,thereby reducing surgical time. The distal ends of threads 114 and 116may taper in diameter toward shaft 102 as they approach imaginary plane110 or, as illustrated, may terminate at plane 110 exposing a face 120.

[0038] Threads 114 and 116 also may be suitably finished to minimizestress on the bony material as screw 100 is inserted therein. Inaccordance with an exemplary embodiment of this aspect of the presentinvention, the outer surfaces or edges of threads 114, 116 are optimallyrounded or smoothed. As will be appreciated, such finish can beengendered through electro-polishing, fine bead sanding or the like.

[0039] With continued references to FIG. 1, in accordance with theillustrated embodiment of the invention, each of respective threads 114and 116 preferably comprise an angled helical upper surface 122, anangled helical under surface 124 and a helical edge 126 interconnectingsurfaces 122 and 124. The thickness T₁ of helical edge 126 of majorthread 114 is greater than the thickness T₂ of helical edge of minorthread 116. Threads of different thicknesses prevent “cross-threading”of the screw as it is rotated into a pre-drilled implantation site. Theterm “cross-threading” refers to an objectionable state where a firstthread of the screw has begun to advance into a pre-drilled thread trackin the implantation site that does not correspond to the first thread.Cross-threading requires higher insertion torques to drive the screwbecause the larger diameter threads must displace bone as the screwadvances. If the screw is made of a polymer, it may not have the shearstrength to withstand such stresses. If the different thread series aredifferent in thicknesses, cross-threading cannot occur.

[0040] Preferably, surface 124 is downwardly angled from the outer edgeof threads 114 and 116 to the body of shaft 102. This angle isillustrated by dimension D. Similarly, upper surface 122 is preferablyangled upwardly from the helical edge 126 of threads 114, 116 to thebody of shaft 102, as is illustrated by dimension E. It should be notedthat the angles of the upper and lower surfaces of the major threads 114may differ from those of minor threads 116 depending on the particularthread configuration. Further, the angles of the upper and lowersurfaces of at least one of the threads 114, 116 may also vary alongshaft 102. Similarly, the thicknesses T₁ and/or T₂ may increase ordecrease along shaft 102, as discussed in more detail below withreference to FIG. 8.

[0041] Referring again to FIG. 1, head 104 at the proximate end of screw100 is designed to fit the head of a driver device. Head 104 may be of asquare, rectangular or hexagonal shape or, alternatively, may be of anyshape suitable to engage a driver for rotation of screw 100.

[0042] In further embodiments, head 104 may include an eyelet 128 ofsufficient size to receive one or more sutures. Eyelet 128 may be of anysuitable size to accept any suture material or may come in a range ofsizes specific to different suture types. In alternative embodiments,head 104 may include a plurality of eyelets to enable one or moresutures to pass through two or more such eyelets.

[0043] In accordance with a further aspect of the present invention,screw 100 may be advantageously made from any suitable bio-compatiblematerial, for example, titanium alloy, stainless steel, class siximplant grade plastic, and the like, or any other bio-compatiblematerial which exhibits adequate pullout strength and has sufficientlylow brittleness to avoid breakage during long term usage of the devicein suture. Alternatively, if screw 100 will be used for an applicationthat does not require a relatively long useful life of the screw, screw100 may be made from a suitable bio-absorbable material, for example,polylactic, polyoxalic or polyglycolic acids or the like.

[0044] As noted above, distal guiding tip 108 serves as a guiding oralignment device that aids a surgeon in guiding and aligning screw 100to a pre-tapped/pre-drilled implantation site. The portal of entry ofscrew 100 may not be perfectly aligned with the implantation site. Asshown in FIG. 2a, it may be difficult for the surgeon to align screw 100to the implantation site as screw 100 often must pass through multiplelayers of soft tissue 204. Thus, screw 100 and a driver 202, incombination, may approach the implantation site 206 at an angle θ(theta) rather than approaching the site in alignment with thelongitudinal axis of the site. FIG. 2b shows screw 100, in combinationwith driver 202, in alignment with implantation site 206. The surgeontypically will use the driver device 202 and screw 100 in combination tomove the tissue 204 and guide screw 100 into the pre-drilledimplantation site 206. By using distal guiding tip 108, the surgeon isable to locate the opening of implantation site 206 and insert distalguiding tip 108 into implantation site 206. The surgeon may then exert amoment on screw 100 and driver device 202, using the outside diametersurface of distal guiding tip 108 and the inside diameter of the core ofimplantation site 206 as bearing surfaces, thereby reducing movement ofscrew 100 and flexion of screw 100 as it enters implantation site 206 sothat screw 100 can advance into the site with little resistance.

[0045]FIG. 3 shows in further detail implantation of screw 100 intoimplantation site 206. Implantation site has been pre-tapped/pre-drilledwith tracks that correspond to the threads 114, 116 of screw 100. In oneembodiment of the invention, all features of implantation site 206 areappropriately 90% of the size of screw 100, except for the core 208 ofimplantation site 206. The diameter of core 208 may be equal to thediameter of shaft 102 of screw 100. The advantage of this feature isthat, as the screw is driven into the bone, the screw threads displacebone, increasing the localized bone density (known in the art as “radialosteo-compression”) without over stressing screw 100 upon implantation.In other alternative embodiments, the-dimension of implantation site 206may be equal to, smaller than or slightly larger than the dimensions ofscrew 100.

[0046] With continued reference to FIG. 3, the length L of distalguiding tip 108 may be equal to or greater than the distance 210 betweenthread centers, although it is desirable that distal guiding tip 108 notbe so long as to require a corresponding implantation site thatsacrifices an unnecessary amount of bone. With length L of distalguiding tip 108 equal to at least the distance between two adjacentthread centers, the distal guiding tip 108 contacts three or more pointslocated in an imaginary cylindrical plane of core 208, therebyconstraining screw 100 from lateral or side-to-side movement.

[0047] As shown in FIG. 3, distal guiding tip 108 terminates at apointed tip. The taper of the pointed tip may be 90° or less as measuredfrom an axis parallel to the longitudinal axis of shaft 102.Alternatively, distal guiding tip 108 may terminate in a beveled tip, asshown in FIG. 1.

[0048]FIGS. 4a and 4 b show an alternative embodiment of the inventionhaving a counter-rotation channel 402. Counter-rotation channel 402 hasa length 406, and a width 404. Counter-rotation channel also has a depth408 that intersects threads 114, 116 and may also intersect a portion ofshaft 102. As bone heals, trabeculae grows into counter-rotation channel402 increasing the torque required to unscrew screw 100 from the bone,thereby reducing the likelihood that screw 100 will loosen from theimplantation site. While FIGS. 4a and 4 b show screw 100 with onecounter-rotation channel 402, it will be appreciated that screw 100 mayhave more than one counter-rotation channel to further reduce thelikelihood that screw 100 will loosen from the implantation site. Asshown in FIGS. 5a-5 e, screw 100 may have two or more counter-rotationchannels 402. However, if more than one counter-rotation channel isemployed, it is preferable that the multiple channels be spaced equallyapart around shaft 102 so as to maintain the balance of screw 100 as itis rotated into an implantation site.

[0049] Referring momentarily to FIGS. 11a and 11 b, an alternativeembodiment of the invention, screw 1100, is shown having at least onecounter-rotation channel 1102. Counter-rotation channel 1102 has alength 1106 and a depth 1108 that intersects threads 114, 116 and mayalso intersect a portion of shaft 102. Screw 1100 further has a slot1112 for receiving internally a driving device for advancing andsecuring screw 1100 into a pre-drilled/pre-tapped implantation site.Screw 1100 may also have at least one eyelet 1110 for receiving sutures.Eyelet 1110 extends through shaft 102 perpendicular to the longitudinalaxis of shaft 102 and the longitudinal axis of the counter-rotationchannel. Eyelet 1110 is positioned below slot 1112 and may be positionedwithin threaded portion 106 or along the distal guiding tip 108.

[0050] Referring to FIGS. 6a-6 c, screw 100 may have counter-rotationelements in addition to counter-rotation channels 402. In FIG. 6a, atleast one of threads 114, 116 may have at least one edge or “tooth” 602.Tooth 602 is integral with the thread but rises adjacentcounter-rotation channel 402 at an angle α (alpha) beyond angle E ofupper surface 122. Angle α is preferably in a range of about 1 degree to45 degrees. Alternatively, tooth 602 may be integral with under surface124 and may extend an angle β (beta) above an axis perpendicular to thelongitudinal axis 112 of shaft 102. As screw 100 is rotated into place,the surrounding bone compresses and deforms around the threads. Oncescrew 100 is in place, the bone decompresses and surrounds screw 100.Tooth 602 will prevent counter-rotation of screw 100 by effectingresistance against the bone of the implantation site which surroundsscrew 100. In an alternative embodiment, as shown in FIGS. 5d and 6 b,screw 100 may have multiple counter-rotation channels 402 and one ormore teeth 602.

[0051] Referring to FIGS. 5e and 6 c, a further embodiment of thepresent invention includes spring-loaded thread members 604 with teeth602. As shown in FIG. 5e, spring-loaded thread members 604 are connectedto shaft 102 by connector members 606. Spring-loaded thread members 604have two fingers 608 that are integrally connected at one end, which endis connected to shaft 102 by connector member 606, and that terminate attheir respective ends at teeth 602. When screw 100 is rotated into theimplantation site, fingers 608 are forced slightly together by bone.During healing, bone grows into counter-rotation channel 402 and intothe space between fingers 608. When torque is applied to screw 100 in acounter-rotation direction, the bone between fingers 608 spreads fingers608 apart, thereby exposing teeth 602 which resist counter-rotation.

[0052]FIG. 7 shows an alternative embodiment of the invention, a screw700. In this embodiment, screw 700 has a tapered shaft 702 from a head704 to the distal end of a distal guiding tip 708, terminating in apointed tip 710. A threaded portion 706 of screw 700 has major threads714 and minor threads 716. Major threads 714 decrease in thickness alongshaft 702, from a thickness T₃ proximate to head 704 to a thickness T₆proximate distal guiding tip 708. While only thread 714 is shown todecrease in thickness, it will be appreciated that thread 716 couldlikewise decrease in thickness along shaft 702. Head 704 has two eyelets728 for receiving sutures. Alternatively, head 704 may have one, threeor more eyelets for receiving sutures.

[0053] In a further alternative embodiment, referring to FIG. 8, a screw800 may have a shaft 802 which is predominantly cylindrical in shape andterminates in a beveled tip 818. A threaded portion 806 of screw 800 hasmajor threads 814 and minor threads 816. Threads 814, 816 both decreasein thickness from proximate a head 804 to proximate a distal guiding tip808. While only two threads, threads 814, 816, are shown, it will beappreciated that screw 800 may have one, three, four or more threads.Head 804 has one eyelet 828, although head 804 may have any number ofeyelets.

[0054] In another embodiment of the present invention, as shown in FIG.9, a screw 900 may have a shaft 902 which is predominantly cylindricaland terminates in a beveled tip 918. Alternatively, shaft 902 mayterminate in a tapered tip. A threaded portion 906 of screw 900 hasmajor threads 914 and minor threads 916. Threads 914, 916 taper indiameter from a larger diameter proximate to a head 904 to a smallerdiameter proximate to a distal guiding tip 908. Threads 914, 916 taperby an angle γ (gamma) measured from a longitudinal axis 912 of shaft902, increasing radial osteo-compression and thus increasing resistanceto pull-out of screw 900. While shaft 902 is shown as cylindrical inshape, it will be appreciated that shaft 902 could taper from proximatehead 904, to the distal end of threaded portion 906. Alternatively,shaft 902 may taper continuously from proximate head 904 terminating ina pointed tip at the distal end of a distal guiding tip 908. Further,although threads 914, 916 are shown with constant thickness along shaft902, either thread 914 or 916 or both may decrease in thickness alongshaft 902 from head 904 to proximate distal guiding tip 908.

[0055] Referring now to FIG. 10, another embodiment of the presentinvention, a screw 1000, has a shaft 1002 which is predominantlycylindrical in shape and terminates in a beveled tip 1018. Screw 1000comprises a first threaded portion 1006 a and a second threaded portion1006 b. Major threads 1014 and minor threads 1016 extend from proximatea head 1004 through threaded portions 1006 a, 1006 b and terminateproximate to distal guiding tip 1008. Threads 1014, 1016 have constantdiameters in first threaded portion 1006 a but taper continuously fromproximate first threaded portion 1006 a through second threaded portion1006 b. While shaft 1002 is shown as predominantly cylindrical, it willbe appreciated that shaft 1002 may taper continuously from the distalend of first threaded portion 1006 a through second threaded portion1006 b. Alternatively, shaft 1002 may taper from the distal end of firstthreaded portion 1006 a through second threaded portion 1006 b anddistal guiding tip 1018, terminating in a pointed tip. In a furtherembodiment, shaft 1002 may taper from head 1004 along the entire lengthof shaft 1002, terminating in a pointed tip. Similarly, it will beappreciated that, while threads 1014, 1016 are shown with constantthickness, threads 1014, 1016 may decrease in thickness in firstthreaded portion 1006 a and/or second threaded portion 1006 b.

[0056] Although the subject invention has been described herein inconjunction with the appended drawing Figures, it will be appreciatedthat the scope of the invention is not so limited. Various modificationsin the arrangement of the components discussed and the steps describedherein for using the subject device may be made without departing fromthe spirit and scope of the invention as set forth in the appendedclaims.

We claim:
 1. A medical screw comprising: a head for receiving a screwdriving device; and a shaft having a length and extending from saidhead, wherein said shaft includes a threaded portion and a distalguiding tip for introducing said screw into a pre-drilled implantationsite.
 2. The medical screw of claim 1 wherein said threaded portion ofsaid medical screw comprises a first series of helical threads having afirst diameter and a second series of helical threads interleaved withsaid first series of helical threads and having a second diameter,wherein said second diameter is different from said first diameter. 3.The medical screw of claim 1 wherein said distal guiding tip terminatesin a point.
 4. The medical screw of claim 1 wherein said distal guidingtip terminates in a beveled face.
 5. The medical screw of claim 1wherein said head is configured as one of a hexagon, square andrectangular head.
 6. The medical screw of claim 1 wherein said headcomprises at least one eyelet for receiving sutures.
 7. The medicalscrew of claim 1 wherein said medical screw further comprises at leastone counter-rotation channel, wherein said counter-rotation channel isconfigured to receive bone growth.
 8. The medical screw of claim 7wherein said medical screw further comprises at least onecounter-rotation tooth, wherein said counter-rotation tooth is proximatesaid counter-rotation channel.
 9. The medical screw of claim 1 whereinsaid shaft is cylindrical.
 10. The medical screw of claim 1 wherein saidshaft tapers from said head and terminates in a point.
 11. The medicalscrew of claim 1 wherein said shaft comprises a cylindrical portion anda tapered portion.
 12. The medical screw of claim 2 wherein at least oneof said first series and said second series of helical threads tapersfrom said head along said shaft.
 13. The medical screw of claim 2wherein the thickness of at least one of said first series and saidsecond series of helical threads decreases along a portion of saidshaft.
 14. The medical screw of claim 2 wherein said first series ofhelical threads has an upper surface configured at a first angle to saidshaft and an under surface configured at a second angle to said shaft,said second series of helical threads has an upper surface configured ata first angle to said shaft and an under surface configured at a secondangle to said shaft, and wherein at least one of said first angle andsaid second angle of said first series of helical threads is differentfrom at least one of said first angle and said second angle of saidsecond series of helical threads.
 15. The medical screw of claim 2wherein said first and second series of helical threads have an uppersurface configured at a first angle to said shaft and an under surfaceconfigured at a second angle to said shaft and wherein at least one ofsaid first angle and said second angle of said first series of helicalthreads and said first angle and said second angle of said second seriesof helical threads changes along said shaft.
 16. The medical screw ofclaim 1 wherein said threaded portion of said medical screw comprises aseries of helical threads which changes in diameter along said shaft.17. The medical screw of claim 2 wherein said first series of helicalthreads has a first pitch and said second series of helical threads hasa second pitch and wherein at least one of said first pitch and saidsecond pitch varies along said shaft.
 18. A medical screw comprising: ahead for receiving a screw driving device; and a shaft having a lengthand extending from said head, wherein said shaft includes a threadedportion and a counter-rotation channel configured to receive bonegrowth.
 19. The medical screw of claim 18 wherein said shaft furthercomprises a distal guiding tip proximate to said threaded portion andconfigured to introduce said medical screw into a pre-drilledimplantation site.
 20. The medical screw of claim 18 wherein saidthreaded portion of said medical screw comprises a first series ofhelical threads having a first diameter, and a second series of helicalthreads interleaved with said first series of helical threads and havinga second diameter wherein said second diameter is different from saidfirst diameter.
 21. The medical screw of claim 19 wherein said distalguiding tip terminates in a point.
 22. The medical screw of claim 19wherein said distal guiding tip terminates in a beveled face.
 23. Themedical screw of claim 18 wherein said head is configured as one of ahexagon, square and rectangular head.
 24. The medical screw of claim 18wherein said head comprises at least one eyelet for receiving sutures.25. The medical screw of claim 18 wherein said medical screw furthercomprises at least one counter-rotation tooth, wherein saidcounter-rotation tooth is proximate said counter-rotation channel. 26.The medical screw of claim 18 wherein said shaft is cylindrical.
 27. Themedical screw of claim 18 wherein said shaft tapers from said head andterminates in a point.
 28. The medical screw of claim 18 wherein saidshaft comprises a cylindrical portion and a tapered portion.
 29. Themedical screw of claim 20 wherein said at least one of said first seriesand said second series of helical threads tapers from said head alongsaid shaft.
 30. The medical screw of claim 20 wherein the thickness ofat least one of said first series and said second series of helicalthreads decreases along a portion of said shaft.
 31. The medical screwof claim 20 wherein said first series of helical threads has an uppersurface configured at a first angle to said shaft and an under surfaceconfigured at a second angle to said shaft, said second series ofhelical threads has an upper surface configured at a first angle to saidshaft and an under surface configured at a second angle to said shaft,and wherein at least one of said first angle and said second angle ofsaid first series of helical threads is different from at least one ofsaid first angle and said second angle of said second series of helicalthreads
 32. The medical screw of claim 20 wherein said first and secondseries of helical threads have an upper surface configured at a firstangle to said shaft and an under surface configured at a second angle tosaid shaft and wherein at least one of said first angle and said secondangle of said first series of helical threads and said first angle andsaid second angle of said second series of helical threads changes alongsaid shaft.
 33. The medical screw of claim 18 wherein said threadedportion of said medical screw comprises a series of helical threadswhich changes in diameter along said shaft.
 34. The medical screw ofclaim 20 wherein said first series of helical threads has a first pitchand said second series of helical threads has a second pitch and whereinat least one of said first pitch and said second pitch varies along saidshaft.
 35. A medical screw having a shaft, wherein said shaft comprises:a threaded portion; a distal guiding tip adjacent said threaded portionwherein said distal guiding tip is configured to introduce said screwinto a pre-drilled implantation site; and a slot for receiving a screwdriving device.
 36. The medical screw of claim 35 wherein said threadedportion of said medical screw comprises a first series of helicalthreads having a first diameter and a second series of helical threadsinterleaved with said first series of helical threads and having asecond diameter, wherein the second diameter is different from saidfirst diameter.
 37. The medical screw of claim 35 wherein said distalguiding tip terminates in a point.
 38. The medical screw of claim 35wherein said distal guiding tip terminates in a beveled face.
 39. Themedical screw of claim 35 wherein said medical screw further comprisesat least one counter-rotation channel, wherein said counter-rotationchannel is configured to receive bone growth.
 40. The medical screw ofclaim 35 wherein said shaft further comprises at least one eyelet forreceiving sutures.
 41. The medical screw of claim 39 wherein saidmedical screw further comprises at least one counter-rotation tooth,wherein said counter-rotation tooth is proximate said counter-rotationchannel.
 42. The medical screw of claim 35 wherein said shaft iscylindrical.
 43. The medical screw of claim 35 wherein said shaft tapersand terminates at a point.
 44. The medical screw of claim 35 whereinsaid shaft comprises a cylindrical portion and a tapered portion. 45.The medical screw of claim 36 wherein said shaft has a proximate end anda distal end and wherein at least one of said first series and saidsecond series of helical threads tapers from said proximate end toadjacent said distal end of said shaft.
 46. The medical screw of claim36 wherein the thickness of at least one of said first series and saidsecond series of helical threads decreases along a portion of saidshaft.
 47. The medical screw of claim 36 wherein said first series ofhelical threads has an upper surface configured at a first angle to saidshaft and an under surface configured at a second angle to said shaft,said second series of helical threads has an upper surface configured ata first angle to said shaft and an under surface configured at a secondangle to said shaft and wherein at least one of said first angle andsaid second angle of said first series of helical threads is differentfrom at least one of said first angle and said second angle of saidsecond series of helical thread.
 48. The medical screw of claim 36wherein said first and second series of helical threads has an uppersurface configured at a first angle to said shaft and an under surfaceconfigured at a second angle to said shaft and wherein at least one ofsaid first angle and said second angle of said first series of helicalthreads and said first angle and said second angle of said second seriesof helical threads changes along said shaft.
 49. The medical screw ofclaim 35 wherein said threaded portion of said medical screw comprises aseries of helical threads which changes in diameter along said shaft.50. The medical screw of claim 36 wherein said first series of helicalthreads has a first pitch and said second series of helical threads hasa second pitch and wherein at least one of said first pitch and saidsecond pitch varies along said shaft.
 51. A medical screw having a shaftcomprising: a thread portion; at least one counter-rotation channelconfigured to receive bone growth; and a slot for receiving a screwdriving device.
 52. The medical screw of claim 51 wherein said threadedportion of said medical screw comprises a first series of helicalthreads having a first diameter, and a second series of helical threadsinterleaved with said first series of helical threads and having asecond diameter wherein said second diameter is different from saidfirst diameter.
 53. The medical screw of claim 51 wherein said shaftfurther comprises at least one eyelet for receiving sutures.
 54. Themedical screw of claim 51 wherein said shaft further comprises at leastone counter-rotation tooth, wherein said counter-rotation tooth isproximate said counter-rotation channel.
 55. The medical screw of claim51 wherein said shaft is cylindrical.
 56. The medical screw of claim 51wherein said shaft tapers and terminates at a point.
 57. The medicalscrew of claim 51 wherein said shaft comprises a cylindrical portion anda tapered portion.
 58. The medical screw of claim 52 wherein said shafthas a proximate end and a distal end and wherein at least one of saidfirst series and said second series of helical threads tapers from saidproximate end to adjacent said distal end of said shaft.
 59. The medicalscrew of claim 52 wherein the thickness of at least one of said firstseries and said second series of helical threads decreases along aportion of said shaft.
 60. The medical screw of claim 52 wherein saidfirst series of helical threads has an upper surface configured at afirst angle to said shaft and an under surface configured at a secondangle to said shaft, said second series of helical threads has an uppersurface configured at a first angle to said shaft and an under surfaceconfigured at a second angle to said shaft, and wherein at least one ofsaid first angle and said second angle of said first series of helicalthreads is different from at least one of said first angle and saidsecond angle of said second series of helical threads.
 61. The medicalscrew of claim 52 wherein said first and second series of helicalthreads has an upper surface configured at a first angle to said shaftand an under surface configured at a second angle to said shaft andwherein at least one of said first angle and said second angle of saidfirst series of helical threads and said first angle and said secondangle of said second series of helical threads changes along said shaft.62. The medical screw of claim 51 wherein said threaded portion of saidmedical screw comprises a series of helical threads which changes indiameter along said shaft.
 63. The medical screw of claim 52 whereinsaid first series of helical threads has a first pitch and said secondseries of helical threads has a second pitch and wherein at least one ofsaid first pitch and said second pitch varies along said shaft.
 64. Amethod of installing a medical screw comprising the steps of: providinga medical screw having a head for receiving a screw driving device and ashaft having a length and extending from said head, wherein said shaftincludes (a) a distal guiding tip for introducing said screw into apre-dilled implantation site and (b) a threaded portion, wherein saidthreaded portion comprises a first series of helical threads having afirst diameter and a second series of helical threads interleaved withsaid first series of helical threads and having a second diameter,wherein said second diameter is different from said first diameter;drilling an implantation site into bone at a desired location; andinserting said distal guiding tip into said implantation site androtating said medical screw to a desired degree of installation.
 65. Amethod of installing a medical screw comprising the steps of: providinga medical screw having a shaft comprising a proximate end and a distalend, wherein said shaft includes (a) a threaded portion and (b) acounter-rotation channel configured to receive bone growth; drilling animplantation site into bone at a desired location, and inserting saiddistal end of said shaft into said implantation site and rotating saidmedical screw to a desired degree of installation.
 66. A method ofinstalling a medical screw comprising the steps of: providing a medicalscrew having a shaft, wherein said shaft comprises (a) a threadedportion wherein said threaded portion comprises a first series ofhelical threads having a first diameter and a second series of helicalthreads interleaved with said first series of helical threads and havinga second diameter wherein said second diameter is different from saidfirst diameter, (b) a distal guiding tip adjacent said threaded portionwherein said distal guiding tip is configured to introduce said screwinto a pre-drilled implantation site, and (c) a slot for receiving ascrew driving device; drilling an implantation site into bone at adesired location; and inserting said distal guiding tip into saidimplantation site and rotating said medical screw to a desired degree ofinstallation.